Apply piston seal for a clutch

ABSTRACT

An apply piston seal is provided for a clutch assembly utilizing a balance piston. The apply piston seal is bonded to the apply piston and provides a sealing relationship between the apply piston and balance piston. By bonding the seal to the apply piston, the manufacturing of the balance piston can be simplified in order to reduce cost for the overall clutch assembly.

FIELD OF THE INVENTION

The present invention relates to a clutch assembly, and moreparticularly, to a clutch and balance piston assembly having a sealdisposed between the apply piston and balance piston.

BACKGROUND AND SUMMARY OF THE INVENTION

In a typical clutch assembly for an automatic transmission (asillustrated in FIG. 8), a clutch pack 16 is provided for providing africtional engagement between a first member 12 and a second member 14which is rotatable relative to the first member 12. A piston 122 isprovided within a fluid chamber 24 such that the application of fluidpressure to the fluid chamber 24 causes the piston 122 to move intoengagement with the clutch pack 16 to frictionally engage the secondmember 14 to the first member 12. The contacting of the friction plateswith increasing pressure eventually causes the rotation of the secondrotatable member 14 which the system is designed to engage. A problemthat has been recognized in the art for a typical clutch assembly ofthis type is that the centrifugal force of the fluid can put a positivepressure on the apply piston 122 as illustrated in FIG. 8. The pressuregenerated by the centrifugal force of the fluid can cause unintendedengagement of the clutch pack 16.

Thus, a balance piston system has been developed as illustrated in FIG.9 in which the balance piston 128 is disposed between the apply piston122 and the clutch pack 16 so that hydraulic fluid is present onopposite sides of the apply piston 122. When the balance piston systemis spinning, the balance piston 128 traps fluid at the outer edge of thecavity 130 that it creates with the apply piston 122 to counteract thecentrifugal forces caused by the fluid on the other side of the applypiston 122 as illustrated in FIG. 9. The balance piston 128 is providedwith a seal member 126 that is bonded to an outer edge 122B and contactsan inner surface of the axially extending arm 122B of the apply piston122. This seal is critical for the proper functioning of the balancepiston system. With the seal 126 applied to the outer surface of thebalance piston 128, the complexity and cost of the manufacture of thebalance piston 128 is significantly increased.

The present invention provides a balance piston/apply piston assemblythat differs from typical assemblies in that the sealing elastomer (orother material) which is used to create the seal between the balancepiston and the apply piston is bonded to the apply piston, not thebalance piston as in typical assemblies. The fact that all of the rubbermolding occurs on the apply piston, and none on the balance piston,provides a significant cost advantage over the typical assembly designwhere rubber must be molded to both components. With this invention, thebalance piston's fabrication does not require adhesive or molding ofrubber, and thus, no quality processes are required relating to apost-molded rubber inspection.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view of a clutch and balance piston assemblyincorporating a seal according to the principles of the presentinvention;

FIG. 2 is a cross-sectional view illustrating the forming of apre-molded slab portion on the apply piston;

FIG. 3 is a cross-sectional view illustrating the cutting process forforming the lip profile into the premolded slab portion of the sealprovided on the apply piston according to the principles of the presentinvention;

FIG. 4 is a cross-sectional view of an apply piston having analternative seal design including a seal skirt according to theprinciples of the present invention;

FIG. 5 illustrates the apply piston and seal shown in FIG. 4 incombination with a balance piston according to the principles of thepresent invention;

FIG. 6 illustrates a cross-sectional view of a second alternativeembodiment of an apply piston and seal arrangement bonded to the applypiston according to the principles of the present invention;

FIG. 7 is a cross-sectional view showing the apply piston and seal asshown in FIG. 6 in combination with a balance piston according to theprinciples of the present invention;

FIG. 8 is a cross-sectional view of a conventional clutch system with anapply piston; and

FIG. 9 is a cross-sectional view of a prior art clutch system having anapply piston and balance piston.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiment(s) is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses.

With reference to FIGS. 1–3, the clutch assembly 10, according to theprinciples of the present invention, will now be described. The clutchassembly 10 includes a first member 12 and a second member 14 rotatablerelative to the first member 12. A clutch pack 16 includes a pluralityof clutch plates 18 having external splines which engage internalsplines of the first member 12 and a plurality of clutch plates 20having internal splines connected to external splines of rotatablesecond member 14. An apply piston 22 is provided in a piston chamber 24provided in the first member 12. The apply piston includes a radiallyextending hub portion 22A and an axially extending arm portion 22B whichpresses against the clutch pack 16. A seal 26 is provided on an innersurface of the axially extending arm portion 22B and includes a moldedslab body portion 26A and a lip profile 26B.

A balance piston 28 is provided between the clutch pack 16 and the applypiston 22. The balance piston includes an inner hub portion 28A with acentral aperture 30 which is received on the shaft portion of member 12.The balance piston 28 is disposed against a stop ring 32 and includes aspring seat portion 34 against which a return spring assembly 36 isdisposed. Return spring assembly 36 also presses against the radiallyextending hub portion 22A of the apply piston in order to bias the applypiston to a disengaged position. Hydraulic pressure generated in thepiston chamber 24 causes the apply piston 22 to move against the biasingforce of the spring assembly 36 and into engagement with clutch pack 16for causing frictional engagement between first member 12 and rotatablymember 14. The balance piston 28 includes an axially extending outerportion 28B which is disposed against the seal lip profile 26B of seal26. The seal 26, along with balance piston 28 and apply piston 22 definea balance chamber 29 that offsets the pressure generated by thecentrifugal force on the fluid in the piston chamber 24.

With reference to FIGS. 2 and 3, a method of forming the seal 26,according to the principles of the present invention, will now bedescribed. As shown in FIG. 2, a molded slab of rubber 38 is formed tothe interior surface of the axially extending arm portion 22B of theapply piston 22. It is noteworthy at this point that the apply pistonalso includes a molded-on exterior seal 40, and that the molded slab 38and seal 40 can be applied simultaneously in a single mold cavity. Withreference to FIG. 3, a trimming process is illustrated for forming thelip profile 26B in the seal 26. A blade 42, as is know in the art, isused for creating the lip profile 26B. It is noteworthy at this pointthat the exterior seal 40 typically requires cutting in a post-moldedstate to remove material flash typically created at the exterior seal40, and that the cutting process for the exterior seal 40 and interiorseal 26 can be performed simultaneously without a significant increasein cost. By placing the seal 26 on the apply piston 22 as opposed to theprior art technique of applying a seal to the balance piston 28, thecost of manufacturing the balance piston 28 is greatly reduced while thecost of manufacturing the apply piston 22 is insignificantly affectedsince molding processes and trimming processes are already required forthe apply piston 22.

With reference to FIGS. 4 and 5, an alternative seal 50 is shown appliedto the interior surface of the axially extending arm portion 22B of theapply piston 22. The seal 50 includes a body portion 51 which is bondedto the apply piston 22 and includes an axially extending skirt 52extending from an end of the body portion 51. As illustrated in FIG. 5,the balance piston 28′ includes a generally J-shaped end portion 54 inwhich the axially extending skirt 52 is received. The post-moldedoutside diameter of the lip is designed to interfere with the outsidediameter of the balance piston. The slight stretching of the rubber“skirt” 52 is meant to be a means by which the contact between therubber and the balance piston is maintained. Since only positivepressure occurs in the cavity between the apply piston and the balancepiston, this pressure tends to maintain the position of the rubber“skirt” 52.

With reference to FIGS. 6 and 7, a second alternative embodiment of thepresent invention will now be described. With reference to FIG. 6, aseal 60 includes a body portion 62 which is bonded to the interiorsurface of the axially extending arm portion 22B of the apply piston 22.An axially extending lip portion 64 extends from the body portion 62 andincludes a recess portion 66 on the radially outer surface thereof. Thelip 64 is bent radially inward and mated with an exterior surface 68 ofa balance piston 28″. The lip portion 64 can be bonded to the balancepiston 28″ by adhesives or otherwise fastened thereto. The sealconfigurations of FIGS. 5 and 7 allow relative axial movement betweenthe balance piston and apply piston while still maintaining a sealedrelationship therebetween. The function of each of the seal systems ofFIGS. 5 and 7 operates the same as the seal 26 as discussed above withrespect to FIG. 1.

The description of the invention is merely exemplary in nature and,thus, variations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the spirit and scope of theinvention.

1. A clutch assembly, comprising: a first member; a second memberrotatable relative to said first member; a clutch pack including atleast one first clutch disc attached to said first member and at leastone second clutch disc attached to said second member; an apply pistonoperable for applying axial pressure on said clutch pack, said applypiston including a radially extending hub portion and an axiallyextending arm portion an end of which is disposed against said clutchpack, said apply piston having a seal bonded to an inner surface of saidaxially extending arm portion, said seal includes an annular lip profileextending radially inward from an annular seal body; and a balancepiston disposed between said apply piston and said clutch pack, saidbalance piston having an outer surface slidably engaging said lipprofile of said seal.
 2. The clutch assembly according to claim 1,wherein said seal is molded to said inner surface of said axiallyextending arm portion.
 3. A clutch assembly, comprising: a first member;a second member rotatable relative to said first member; a clutch packincluding at least one first clutch disc attached to said first memberand at least one second clutch disc attached to said second member; anapply piston operable for applying axial pressure on said clutch pack,said apply piston including a radially extending hub portion and anaxially extending arm portion an end of which is disposed against saidclutch pack, said apply piston having a seal fixedly disposed on aninner surface of said axially extending arm portion; a balance pistondisposed between said apply piston and said clutch pack, said balancepiston having an outer surface engaging said seal; wherein said sealincludes a lip fastened to said outer surface of said balance piston. 4.A clutch assembly, comprising: a first member; a second member rotatablerelative to said first member; a clutch pack including at least onefirst clutch disc attached to said first member and at least one secondclutch disc attached to said second member; an apply piston operable forapplying axial pressure on said clutch pack, said apply piston includinga radially extending hub portion and an axially extending arm portion anend of which is disposed against said clutch pack, said apply pistonhaving a seal fixedly disposed on an inner surface of said axiallyextending arm portion; a balance piston disposed between said applypiston and said clutch pack, said balance piston having an outer surfaceengaging said seal; wherein said seal includes a lip received in aformed portion of said outer surface of said balance piston.